I set up Cafu from Git relatively painlessly on Debian Linux. I am able to load the executables.

I'm a total beginner with Cafu (and Lua, for that matter), so prepare for a stupid question: what file represents a game? The manual starts with "how to build maps" and not "how to create a game" or "how to run a game."

I'd like to try DeathMatch without downloading a three-year-old version of Cafu just for that purpose. The Git source put a DeathMatch directory on my system, but I see no way to launch the actual game. Loading Cafu works, but the GUI has a disabled Load Game button. I can select New Game and choose a map, but then Go does ... nothing at all?

How can I actually launch DeathMatch? Do I have to compile it myself, which would require ... something? I say that because the User Manual here (http://docs.cafu.de/) doesn't have a section called "compile a game" or "package a game" or "launch a game" anywhere? A search via Google (and its various competitors) also fails to find that information. Maybe a simple document outlining the whole "from concept to packaging the game and letting people play" tutorial would be a good idea?

A game is not represented by a single file, but an entire directory in Games/.

We used to have custom C++ code for each game, but thanks to the entity component system, this is no longer necessary -- the Lua scripting code provides all the glue that is necessary to make a game.

A game is run by running the Cafu executable, selecting a specific game via command line parameter. Run Cafu --help for details, also see this forum post.

The problems that you're experiencing are most likely related to the fact that the Git repository comes with the maps in "source code form" as saved by CaWE in Games/DeathMatch/Maps/*.cmap. The engine however, closely to your supposition, needs "compiled" maps. The first compiler, CaBSP, reads a map from Games/DeathMatch/Maps/ and saves the result at Games/DeathMatch/Worlds/.